Photolithography process is an important process of the semiconductor manufacturing technology, which transfers patterns on a reticle to a substrate by an exposure process. Photolithography process is one of the core steps for the manufacturing of large scale integrations (LSIs).
The development of the photolithography technology has gone through the contact photolithography technology, the proximity photolithography technology, the scanning-projection photolithography technology, the step-and-repeat photolithography technology and the state-of-the-art step-and-scan photolithography technology. The step-and-scan photolithography technology is an advanced technology of the photolithographic fabrication of the integrated circuits (ICs).
In a photolithography process, a silicon wafer (or other substrate) having a photoresist layer is divided by a plurality of exposure shots; the step-and-scan photolithography technology utilizes the synchronic motion of a reticle stage and a wafer stage to project the patterns on the reticle to a single exposure shot. During such a process, the wafer stage moves along the exposure scanning direction of an exposure apparatus. At the same time, the reticle stage moves along a direction opposite to the moving direction of the wafer stage. Thus, a scan-exposure step for the exposure shot is finished. After scanning and exposing the single exposure shot, the wafer stage steps to another exposure shot and perform another scan-exposure process. The step-and-scan process is repeated until all the exposure shots are scanned and exposed. Then, patterns with a certain-time reduced size are formed on the wafer after subsequent fixing and developing process.
FIG. 1 illustrates the exposure process of an existing exposure apparatus. As shown in FIG. 1, the wafer 100 has a plurality of exposure shots. After scanning the first exposure shot 101 in a first direction (the arrow direction), the adjacent second exposure shot 102 is scanned in a second direction opposite to the first direction. Such a process is repeated in a reciprocal way until all the exposure shots on the wafer 100 are exposed.
The scan-exposure process for each of the exposure shots includes three stages: acceleration stage, scanning and exposure stage and de-acceleration stage. The wafer stage and the reticle stage start from a stop status; and accelerate to a predetermined speed after a time range of tac. Then, the wafer stage and the reticle stage start to scan and expose with the constant predetermined speed. After another time range of tsc, the wafer stage and the reticle stage start to de-accelerate. After another time range of tde, the speed of the wafer stage and the reticle stage reaches to zero.
Therefore, in the entire exposure process for a single exposure shot, only the time rang of tsc is for the exposure, the time range of tac and the time range of tde are for assisting the scanning. For example, it needs 0.26 s for scanning and exposing a single exposure shot using a speed of 600 mm/s. During this time range, the acceleration time tac is 0.1 s, the scan and exposure time tsc is 0.06 s; and the de-acceleration time is 0.1 s. That is, the scan and exposure time tsc is only approximately 20% of the total time of the exposure process of a single exposure shot.
Because the scan-exposure process for each of the exposure shots all includes the acceleration time tac, the scan and exposure time tsc and the de-acceleration time tde, the exposure time for an entire wafer may be relatively long and the exposure efficiency of the existing exposure apparatus is relatively low. The disclosed methods and systems are directed to solve one or more problems set forth above and other problems.